The present invention relates generally to hydraulically powered differential steered agricultural machines, and more particularly to an autoguidance interface for a hydraulic steering system for such a machine
Hydrostatic drive systems are often configured with the drive pump attached directly to the engine without a clutch or other mechanism to stop output flow of the pump while the engine is running. Drive pump displacement (output) and therefore speed in differential-steered machines is controlled by variations in swashplate angle which is adjusted by movement of external pintel arms external to the pumps. On most pumps, pintel arm and thus swashplate rotation from “neutral” to “full speed” occurs over a relatively narrow range on the order of 16-18 degrees. With such a small range of motion, it is important that the assembly controlling the angular position of the pintel arm angles be capable of precise angular control. Precise control of the swashplate angle for hydrostatic ground drive pumps on differential-steered agricultural machines is paramount, especially when operating the machine at higher travel speed such as is necessary for road transport between fields.
One common conventional mechanical mechanism uses an input shaft that may be rotated and moved fore-and-aft along its longitudinal axis. Threaded portions on the input shaft, one right-hand threaded and one left-hand threaded, are engaged by mating threaded followers that are connected to the pintel arms on a pair of pumps connected in tandem alongside the input shaft. Rotation of the input shaft result in the followers moving along the threaded portions, either toward each other or away from each other. The result is that the pintel arms are rotated in opposite directions as the input shaft is rotated resulting in opposing changes in the hydraulic pump output to the drive motors (e.g., one increases speed while the other decreases speed). Rotation of the input shaft is directed by a steering wheel located in the operator cab of the machine. Fore and aft movement of the input shaft does not adjust the relative rotational position of the pintel arms, but instead rotates the pintel arms in the same direction by the same degree and is used to adjust the machine travel speed and select between forward and reverse directional movement.
Autoguidance systems are increasingly being fitted to agricultural machines in the quest for ever-improving efficiency. As autoguidance systems become more prevalent in agricultural machines, windrowers and the like are being fitted with autoguidance systems. Incorporating autoguidance systems into an existing machine typically involves the addition of actuators or other mechanical adapters to allow the autoguidance steering actuators to interface with the manual steering system already existing on the machine. Such additions add complexity and cost and may not provide the reliability of a more integrated approach.